Wouldn’t a hybrid system make more sense?

To only assign blame to people/teams when they’ve guaranteed in writing that it would be so and so, avoiding the downsides.

And blaming the process when there were no such guarantees?

The issue with any hybrid system is you have to play the incentives out at scale.

E.g. if blame is assigned when there's a written guarantee, why would anyone ever make a written guarantee?

And not trying to be obtuse, but I've only ever seen blameless cultures work in absolute. Compromises let back in all the nasty mal-incentives you see driving unproductive CYA behaviors.